The present invention relates to a fastener system for multi-piece swage type fasteners, methods of installation and a tool for installing such fasteners.
The present invention relates to two-piece swage type fasteners or lockbolts generally of the type illustrated in U.S. Pat. Nos. 2,531,048 and 2,531,049 to L. Muck both issued on Nov. 21, 1950, and in U.S. Pat. No. 3,915,053 to J. Ruhl, issued Oct. 28, 1975.
Swage type fasteners of the type noted are frequently of a two-piece construction comprising a pin and a collar adapted to be swaged into locking grooves on the pin. The fasteners shown in the referenced '048 and '049 patents are pull type swage fasteners while those shown in the '053 patent include both pull type and stump type versions of swage fasteners. In the typical pull type fastener, the pin is provided with an enlarged head and a pin shank having locking grooves in a lock groove portion; the pin shank terminates in a pintail portion constructed with pull grooves adapted to be gripped by a jaw assembly of an installation tool. A swage anvil is provided on the tool to engage and swage the collar into the locking grooves. A relative axial force is applied between the pin and collar, and hence between workpieces to be fastened together, as the tool pulls on the pin via the pintail portion with the force being reacted by the engagement of the swage anvil with the collar. This relative axial force pulls the workpieces together under an initial clamp load.
As the relative axial load increases the swage anvil moves axially to radially overengage the collar, swaging it into the locking grooves, whereby the pin and collar are locked together and the final clamp load on the workpieces is developed. The swage anvil has a swage cavity which receives the collar circumferentially for 360.degree. and axially over the majority of the length of the collar or collar shank where a flanged collar is employed whereby a substantial portion of the swageable collar material is deformed into the locking grooves of the pin, generally uniformly around its circumference.
The pintail portion is connected to the locking groove portion by a breakneck groove which is constructed to break at a preselected axial load after the swaging step has been completed whereby the pintail portion is severed and discarded.
In the stump type version, the lockbolt is set by a squeeze type tool which has a stationary member at one end of the workpieces for engaging the pin head and a swage anvil at the opposite end for engaging the collar. The fastener is set as the anvil moves axially against and radially over the collar with the axial force being reacted by the engagement of the stationary member with the pin head. Thus the stump type fastener has the advantage of a shorter pin shank since the pintail portion with pull grooves and breakneck groove is not required. Because of the latter the stump version has the advantage of being lighter and of a lower cost.
But there are other advantages of the stump type swage fastener relative to the pull type fastener. With the pull type fastener, the severed pintail portion creates debris in the work area requiring periodic collection and disposal. Also the stump version will assure a smooth, finished end at the pin shank whereas the pull type pin shank will occasionally have a rough surface from the break at the breakneck groove. Finally the noise occasioned by pinbreak is absent in the stump type fastener.
There are, however, numerous applications in which a stump type fastener cannot be used or it is not expedient to do so. One example is an assembly in which there is insufficient clearance on the pin head side of the workpieces to permit access for the related stationary portion of the squeeze tool. Another example is an assembly having insufficient clearance to permit insertion of the longer pull type pin into the mating openings of the workpieces. The present invention addresses such problems. Thus with the present invention a unique fastening system including a swage type fastener and installation tool is provided for a pull type installation but, as will be seen, having advantages of a stump type fastener and installation. Indeed, where both squeeze type and pull type applications and apparatus are present, the fastener of the present invention can be installed in either fashion resulting in a reduction in overall inventory and in the numbers of different parts to be stocked.
Thus the present invention is of a swage type fastener with a pin having a shank constructed without a severable pintail portion but terminating in a short, threaded or other gripable, pull portion of minimal length. A unique tool is shown which functions to provide a pull type installation; the tool includes a threaded, hardened nut member adapted to threadably engage the short pull portion via rotation by a rotary drive motor. Once a sufficient number of threads have been engaged or gripped by the nut member, the pull tool is actuated to apply a relative axial force by pulling on the pin, through the nut member, with a swage anvil engaging the collar to react the pulling force. At this juncture, the fastening system performs similarly to a pull type installation system. Thus as the magnitude of the relative axial force increases the workpieces being secured are pulled and clamped together under a desired preload. Upon further increases in the axial force the anvil will be moved axially to radially overengage the collar and swage it radially into the locking grooves on the pin shank providing the final clamp load. Next the direction of relative axial force between the swage anvil and nut member is reversed moving the swage anvil in the opposite axial direction to thereby eject the swaged collar. Finally, the hardened nut member is reverse rotated from the short, threaded pull portion removing the installation tool and completing the installation. A rotary drive motor in the pull tool is used to thread the nut member onto and off from the threaded pull portion. Thus no pintail portion is required to be removed after swage and hence there is no related debris. In addition the installation is quieter since pinbreak noise is eliminated. The length of pin shank comprising the short, threaded pull portion is minimal, i.e. around four threads, such that only a small difference in length of pin shank remains relative to a comparable stump type pin set by a squeeze tool and/or the pin shank of a pull type fastener after the pintail portion has been removed by a conventional pull type tool.
In one form of the invention the lock grooves and threads of the pull portion of the pin are in the form of a continuous helical male thread. The collar is provided with a mating, female thread of a preselected extent such that an initial clamp of the workpieces can be accommodated. However, the female collar thread is selected to be of a limited circumferential extent and shear strength such that, in response to the relative axial force and at a level prior to the initiation of collar deformation into the lock grooves of the pin, it will shear or deform; in this condition the collar will be generally free to move axially over the pin and to respond to the installation loads in the same manner as a collar without such limited female thread form.
The preceding fastener structure with limited threaded collar is sometimes referred to as a "fit-up fastener" and is shown and described in the U.S. Patent application of R. Dixon for "Variable Clamp Fastener and Method" No. 282,875, Filed Dec. 19, 1988 issued into U.S. Pat. No. 4,867,625 on Sep. 19, 1989 and is incorporated herein by reference; that structure, however can be considered as prior art to the present invention. One advantage of the fit-up fastener structure in a combination in the present invention is that the workpieces can be initially pulled together to remove gap thereby providing greater certainty that a sufficient number of the threads of the pull portion will extend beyond the collar and be accessible for gripping by the nut member.
Alternatively, a collar with a flexible tab can be used for fit-up; such a structure is shown in the U.S. Pat. No. 4,813,834 for "Fit-Up Fastener With Flexible Tab-Like Structure and Method of Making Same" issued Mar. 21, 1989 to Walter J. Smith.
In a preferred form of the invention, the tool nut member is designed simply to threadably engage and thereby grip the minimum length pull portion of the pin; thus, in this first step, the tool nut member is not moved against the collar with any significant force and hence is not used to pull the workpieces together and/or clamp them under an initial preload. After the threaded engagement step, the installation tool is actuated to cause the swage anvil to move axially against the collar in response to a relative axial force applied between the nut member and the anvil. Thus the initial clamp up and preload of the workpieces is substantially provided for the first time by the relative axial force applied between the nut member as engaged with the pull portion of the pin shank and the engagement of the swage anvil with the collar. As previously described, the relative axial force is increased until the swage cavity of the anvil is moved axially to radially overengage the collar swaging the collar material into the pin. With this construction, the rotary drive motor for the nut member simply provides the function of threading the nut member on and off the short pull portion of the pin shank and is not used to apply any significant axial load to the workpieces. Thus the capacity of the drive motor can be small permitting the overall size of the installation tool to be minimized. In one form of the invention, the engagement of the tool nut member on the threaded pull portion is limited and the nut member positioned thereon such that the collar, upon elongation in swage, will essentially not engage the nut member. Thus no significant axial bearing load will be applied against the nut member from collar elongation after swage; this inhibits increases in friction between the engaged threads of the nut member and pull portion which would result from such bearing load. In this way removal torque can be maintained low which also facilitates the use of a rotary motor of minimal size.
Prior crimp type fasteners, while utilizing a pintail-less or stump-like structure would not provide the same advantages and/or ease of installation as the present invention. For example, a threaded crimp type fastener would not provide the same flexibility and ease of installation and would require more complex installation tools. In this regard see the U.S. Pat. No. 3,421,562 to J. Orloff et al issued on Jan. 14, 1969. There a threaded fastener nut or collar is first installed on a threaded pin shank and torqued to provide initial pull together and clamp up of the workpieces of a first magnitude; the final clamp load is achieved by crimping a smooth portion of the nut resulting in elongation of the nut and an increase in clamp load to a desired final magnitude. Thus in the system of the '562 patent the fastener is not set as either a stump type or pull type as described and is unlike the system and fastener of the present invention. In this regard see also the U.S. Pat. No. 3,803,793 to W. Dahl issued on Apr. 16, 1974.
Another crimp type fastener is shown in the U.S. Pat. No. 4,012,828 to W. Dahl issued Mar. 22, 1977. There a threaded mandrel on a tool is first threaded onto a threaded pin shank until the mandrel engages a smooth bored collar to clamp the workpieces together and to apply an initial preload of a first magnitude. Next crimping jaws, spaced radially about the collar, are actuated to move radially inwardly to deform the material of the collar into threads or locking grooves in the pin. The resultant collar elongation reacts between the engaged workpiece and the engaged end of the threaded mandrel to provide an increased clamp load of a final magnitude. After disengaging the crimping jaws, the mandrel is threaded off the pin to complete the installation. Thus, again, in the system of the '828 patent, the fastener is not set as the stump or pull type fastener in the manner previously described and also is unlike the system and fastener of the present invention. See also the U.S. Pat. No. 3,920,338 issued to W. Dahl on Nov. 18, 1975.
The U.S. Pat. No. 3,025,730 issued to H. Brilmyer et al on Mar. 20, 1962 discloses the use of a manual installation tool on a swage fastener having a threaded pintail portion and a breakneck groove with a nut on the tool threadably engageable with the pintail portion. The system and fastener of the '730 patent is also unlike the system and fastener of the present invention.
The U.S. Pat. No. 4,299,519 issued to R. Corbett on Nov. 11, 1981 discloses a fastener with a minimum length removable pintail portion; it also discloses a pin having an internally engageable pull groove structure and no removable pintail portion. That fastener, however, does not disclose the externally, threaded short pull portion nor does it disclose an internally threaded gripping portion.
As will be seen from the description of the embodiments which follows, various combinations of fastener pins and collars can be used with the system and installation tool of the present invention. Thus it is an object of the present invention to provide a unique fastener system including novel swage type fasteners having the advantages of a stump type fastener and being installed generally as a pull type fastener.
It is another object of the present invention to provide a novel fastening system including a unique installation tool for use in setting swage type fasteners.
It is another general object to provide a unique fastening system including a novel swage type fastener and a novel installation tool.